Valorisation of Fly Ash, Ground Granulated Blast Furnace Slag (GGBFS), Silica Fume Along with Graphene in High-Performance Geopolymer Self-Compacting Concrete

Abstract

The high carbon emissions connected with ordinary Portland cement (OPC) production have fuelled the search for sustainable alternatives in the construction industry. Geopolymer concrete (GPC), made from industrial byproducts including fly ash (FA) and ground granulated blast furnace slag (GGBFS), is a low carbon option. This study looks at the use of FA, GGBFS, silica fume (SF), and graphene oxide (GO) in the production of high-performance geopolymer self-compacting concrete (HPGSCC). Two experimental series were developed to assess fresh, mechanical, durability, and microstructural characteristics. In the first series, a reference mix of 50% FA and 50% GGBFS was created, and FA was replaced with SF at 5%, 10%, 15%, and 20% to establish the best replacement level. In the second series, GO was added to the optimum SF-based combination at concentrations ranging from 0.01% to 0.05% by weight of geopolymer paste. European Federation of National Associations Representing for Concrete (EFNARC) recommendations were followed to assess workability through slump flow, T???, V-funnel, L-box, and J-ring tests. Compressive and flexural strength tests were performed at 7 and 28 days to assess hardened characteristics, as well as water absorption and porosity measurements. scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to study the microstructural and mineralogical features. The results show that 15% SF replacement offers the best mechanical per-formance due to improved particle packing and matrix densification. Excessive SF content resulted in a minor strength drop. The addition of GO increased compressive and flexural strength, refined pore structure, and reduced water absorption and po-rosity via enhanced geo-polymerization and interfacial bonding. Although workability declined with increasing SF and GO con-centration because to increased specific surface area and water demand, all optimized mixes met the self-compacting concrete criterion.

Introduction

High-performance geopolymer self-compacting concrete (HPGSCC) is an eco-friendly alternative to conventional Portland cement concrete, developed to reduce CO? emissions associated with cement production. Since cement manufacturing contributes significantly to global greenhouse gas emissions, geopolymer concrete (GPC) is explored as a sustainable substitute by using industrial by-products such as fly ash (FA), ground granulated blast furnace slag (GGBFS), and silica fume (SF). These materials act as aluminosilicate sources and, when activated with alkaline solutions like sodium hydroxide and sodium silicate, form strong binding gels such as C-S-H and N-A-S-H, improving strength and durability.

The study further investigates the use of nano-material graphene oxide (GO), which enhances mechanical properties, crack resistance, and durability even in small quantities. The combination of FA, GGBFS, SF, and GO is used to develop optimized HPGSCC mixes to study their combined effect on concrete performance.

Experimental work includes material selection, mix design variations, specimen preparation, and testing of fresh and hardened properties. Workability tests such as slump flow, V-funnel, L-box, and J-ring were performed to evaluate flowability, passing ability, and segregation resistance. Results show that increasing SF and GO content reduces workability due to higher surface area and water absorption. However, these additions improve mechanical strength and durability characteristics.

Microstructural analysis using XRD and SEM is used to study hydration products and internal structure, while mechanical tests assess compressive strength, flexural strength, water absorption, and porosity. Overall, the study concludes that optimized use of FA, GGBFS, SF, and GO can produce sustainable, high-performance self-compacting geopolymer concrete suitable for future construction applications with reduced environmental impact.

Conclusion

This study focuses on the synergistic effects of FA, GGBFS, SF and GO in producing HPGSCC. Conclusions drawn from experi-mental observations and analytical results are: - 1) Due to their high specific surface area and water demand, the workability of HPGSCC mixtures is found to decrease with in-creasing SF and GO contents with respect to reference mix. Still, all optimized mixes fulfil the EFNARC guidelines for self-compacting concrete except mix GPC-G4 and GPC-G5. 2) The addition of silica fume as a partial replacement for FA greatly improved the mechanical and durability qualities of HPG-SCC. Among the examined mixes, the optimal replacement amount was 15% SF, which resulted in increased compressive and flexural strength due to improved particle packing and matrix density. However, increasing the SF concentration resulted in a slight loss in strength, mostly due to agglomeration of SF particles in the mix and lower workability. 3) The addition of GO enhanced the optimized mix\'s performance qualities. GO helped to increase compressive and flexural strength, minimize water absorption, and reduce porosity. These enhancements are ascribed to better pore structure, geo-polymerization, and interfacial bonding within the matrix. The capacity of GO to fill cracks and bridge them was critical in im-proving the microstructure. 4) Microstructural study using SEM and XRD revealed the development of dense and compact geopolymer matrices containing C-A-S-H and N-A-S-H gels. The addition of SF and GO resulted in a more refined microstructure, fewer voids, and improved in-terfacial transition zones, which were directly associated to improved mechanical and durability performance. 5) Overall, the study shows that combining FA, GGBFS, SF, and GO can result in a sustainable, high-performance construction material with low environmental impact. The proposed HPGSCC has tremendous potential as an alternative to conventional Portland cement-based concrete, helping to promote greener construction practices.

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Copyright

Copyright © 2026 Rakesh Bishnoi, Dr. Hemant Sood, Dr. Lilesh Gautam. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.